Radio frequency identification (RFID) is an area of automatic identification that has been gaining favor among a variety of industry groups in recent years and is now generally recognized as a means of enhancing data handling processes, complimentary in many ways to other data capture technologies such as bar coding. A range of devices and associated systems are available to satisfy a broad range of applications. Despite this diversity, the principles upon which RFID is based are quite straight forward, even though the technology and technicalities concerning the way in which it operates can be quite sophisticated.
The object of any RFID system is to store data in one or more of a variety of transponders, commonly known as tags, and to retrieve this data, by machine-readable means, at a suitable time and place to satisfy particular application needs. Data within a tag may provide identification for an item in manufacture, goods in transit, a location, and/or the identity of an animal or individual. By including additional data the prospect is provided for supporting applications through item-specific information or instructions immediately available upon reading the tag. For example, the color of paint for a car body entering a paint spray area on a production line can be encoded in a tag for reading (and subsequent utilization) as the car body enters the painting area.
In addition to the tags themselves, an RFID system requires some means of reading or interrogating the tags (often called a “reader” although it generally includes some form of transmitter for interrogating the tags) and some means of communicating the data to a host computer or information management system. A system may also include a facility for entering or programming data into the tags, if the manufacturer does not undertake this operation at the source. Quite often an antenna is distinguished as if it were a separate part of an RFID system. While its importance justifies this attention, antennas are perhaps better viewed as features that are present in both readers and tags, essential for the communication between the two.
Communication of data between tags and a reader is by wireless communication. Two common methods distinguish and categorize RFID systems, one based upon close proximity electromagnetic or inductive coupling and one based upon propagating electromagnetic waves. Recently, capacitive coupling schemes have also been introduced. In any event, coupling is via the antenna structures described above and while the term antenna is generally considered more appropriate for propagating systems it is also loosely applied to inductive systems.
FIG. 1A illustrates a conventional RFID system that relies on inductive coupling to transmit stored information to a reader. As shown, the tag 10 is placed so that its antenna 12 is within a radio frequency (RF) field created by the reader's antenna 14. As a current is passed through the antenna 14, the RF field 16 is generated. The area of the RF field 16 will depend on the amount of current passed through antenna 14, the type of materials that are used to construct antenna 14, and the size and type of antenna 14 that is used. As the tag's antenna 12 passes through the RF field 16, a current is generated in the antenna 12 and that current is used to power the tag components, resulting in the stored data being transmitted. If the reader uses a time varying current within antenna 14, this process will occur even if the tag 10 is stationary. Because the tag 10 does not include its own power source to carry out transmissions of data, the tag is referred to as a passive RFID tag.
FIG. 1B illustrates the use of an active tag 18, which allows for coupling through propagating electromagnetic waves. In this case, the tag 18 includes its own power source (e.g., a battery) which allows the tag to transmit its stored data to a reader antenna 20 directly, without having to rely on power generated from a radiated RF field. This allows for reading operations over extended ranges from that usually provided by passive tags that rely on inductive coupling.
To transfer data efficiently via the air that separates the two communicating antennas generally requires that the data be superimposed upon a carrier wave, as is common in the communication arts. This process is referred to as modulation, and various schemes are available for this purpose, each having particular attributes that favor their use. Commonly employed modulation techniques for RFID tags include amplitude shift keying (ASK), frequency shift keying (FSK) and phase shift keying (PSK). Common carrier frequencies include high frequencies (HF, approximately 3-30 MHz), very high frequencies (VHF, approximately 30-300 Mhz) and ultra high frequencies (UHF, frequencies above 300 MHz). Higher carrier frequencies allow for faster data rates, but are generally limited to line-of-sight applications. Commonly used commercial RFID systems operate at 13.56 MHz, while others operate at 915 MHz.
Having looked at some of the basics behind RFID technology, we turn now to some further details regarding the components that make up a conventional system. FIG. 2 illustrates an example of a conventional RFID system 22 that includes a transponder or tag 24 (which may be of the active or passive variety) with an antenna 26, and a reader/programmer 28 with an antenna 30. The word transponder, derived from the combination of TRANSmitter and resPONDER, reveals the function of the device. The tag 24 responds to a transmitted or communicated request for the data it stores by communicating information by wireless means across the space or air interface between the tag and the reader. The term also suggests the essential components that form an RFID system—tags and a reader or interrogator. Where interrogator is often used as an alternative to the term reader, a difference is sometime drawn on the basis of a reader together with a decoder and interface forming the interrogator.
The basic components of tag 24 are shown in FIG. 3. Generally speaking tags are fabricated as low power integrated circuits suitable for interfacing to external coils (i.e., antennas 26), or utilizing “coil-on-chip” technology, for data transfer and power generation (passive mode). Some analog circuitry 32 is generally included for these purposes. In addition, the tag may include a read-only memory (ROM) 34, random access memory (RAM) 36 and/or non-volatile programmable memory (often a form of Flash memory) 38 for data storage depending upon the type and sophistication of the device.
The ROM-based memory 34 is used to accommodate security data and the transponder operating system instructions which, in conjunction with the processor or processing logic 40, deals with the internal “house-keeping” functions such as response delay timing, data flow control and power supply switching. The RAM-based memory 36 may be used to facilitate temporary data storage during transponder interrogation and response. The non-volatile programmable memory 38 may take various forms, electrically erasable programmable read only memory (EEPROM) being typical. It is used to store the transponder data and needs to be non-volatile to ensure that the data is retained when the device is in its quiescent or power-saving “sleep” state.
Various data buffers (which are created in the volatile memory 36) may be used to temporarily hold incoming data following demodulation and outgoing data for modulation and interface with the tag antenna 26 (which itself is used to sense the interrogating field and, where appropriate, the programming field, and also serves as the means of transmitting the tag response to the interrogator). The interface circuitry 32 provides the facility to direct and accommodate the interrogation field energy for powering purposes in passive transponders and triggering of the tag response. Where programming is accommodated, facilities must be provided to accept the incoming data modulated signal and perform the necessary demodulation and data transfer processes.
RFID tags such as tag 24 come in a wide variety of physical forms, shapes and sizes. Animal tracking tags, inserted beneath the skin, can be as small as a pencil lead in diameter and ten millimeters or so in length. Tags can be screw-shaped to identify trees or wooden items, or credit card shaped for use in access applications (e.g., identity badges). The anti-theft hard plastic tags attached to merchandise in stores are a form of RFID tag, as are the heavy-duty rectangular transponders used to track inter-modal containers, or heavy machinery, trucks, and railroad cars for maintenance and tracking applications.
Returning to FIG. 2, the reader/interrogator 28 can differ quite considerably in complexity, depending upon the type of tags being supported and the functions to be fulfilled. However, the overall function is to provide the means of communicating with the tags 24 and facilitating data transfer (a process generally known as “scanning”). Functions performed by the reader 28 may include quite sophisticated signal conditioning, parity error checking and correction. Once the signal from a tag 24 has been correctly received and decoded, algorithms may be applied to decide whether the signal is a repeat transmission, and may then instruct the transponder to cease transmitting. This is known as the “Command Response Protocol” and is used to circumvent the problem of reading multiple tags in a short amount of time. Using interrogators in this way is sometimes referred to as “Hands Down Polling”. An alternative, more secure, but slower tag polling technique is called “Hands Up Polling”, which involves the interrogator looking for tags with specific identities, and interrogating them in turn. This and other contention management techniques have been developed to improve the process of batch reading. A further approach may use multiple readers, multiplexed into one interrogator, but with attendant increases in costs.
Transponder programmers are the means by which data is delivered to tags capable of being programmed/reprogrammed. Programming is generally carried out off-line, at the beginning of a batch production run, for example. However, in some systems reprogramming may be carried out on-line, particularly if a tag is being used as an interactive portable data file within a production environment, for example. By combining the functions of a reader/interrogator and a programmer into a single unit 28, data may be read and appended or altered in the tag 24 as required.
Potential applications for RFID are many and varied. The attributes of RFID are complimentary to other data capture technologies and thus able to satisfy particular application requirements that cannot be adequately accommodate by alternative technologies. Principal areas of application for RFID that can be currently identified include: transportation and logistics, manufacturing and processing, and security. A range of miscellaneous applications may also be distinguished, some of which are steadily growing in terms of application numbers. They include: animal tagging, waste management, time and attendance, postal tracking, and road toll management. As standards emerge, technology develops still further, and cost reduction has spawned considerable growth in terms of application numbers.
One application that has received some attention from developers of RFID systems is that of inventory control. For example, U.S. Pat. No. 6,148,291 to Radican describes container and inventory monitoring methods and systems that provide logistical control of containers, shipping racks and resident and in-transit inventory. The methods and systems create and maintain real-time records of the location, movement and load status of containers, racks and inventory within facility boundaries and between facilities such as factories, assembly plants, warehouses, shipping yards and freight switching facilities. Information regarding container switching, unloading and loading activities is recorded and archived. A virtual inventory accounting is also provided.
Shipping containers, such as those discussed in U.S. Pat. No. 6,148,291, are often employed to transport other items from suppliers to users. Often times, these shipping containers are high value units and sometimes the value of the shipping container exceeds the value of the items being shipped therein. Because of the high value associated with these containers, the users (which need not necessarily be end users of the relevant products but may in fact be vendors thereof) are required to either purchase the shipping container (which purchase price may later be refunded (at least in part) if the container is later returned) or place a security deposit (which also may be refunded upon return of the shipping container) for the container with the supplier. Because manual record keeping is subject to human error, it is often the case that accounts are not properly credited, or that accounts are improperly credited, for the return, or failure to return as the case may be, of the shipping containers. The inventory monitoring and control system proposed in U.S. Pat. No. 6,148,291 does not address this problem.
Likewise, although U.S. Pat. No. 6,169,483 to Ghaffari et al., describes a self-checkout/self-check-in and electronic article surveillance (EAS) system, this system does not address the problem of proper accounting for returned shipping containers and the like. The Ghaffari system combines EAS tags with RFID tags and both are connected to articles of clothing and the like. The RFID tags are read, and after verification of an authorized transaction, a deactivation antenna is energized to deactivate the EAS tags, and a stored inventory database is updated. For returns, articles are deposited in an elongated housing and the RFID tags on the articles are read, the inventory database updated, and an activation antenna is energized to form an activation zone through which the articles pass as they fall through the housing, thus activating the attached EAS tags. In this way, in-store inventories can be updated, but there is no mechanism for automatically crediting customer accounts during a return process.
U.S. Pat. No. 6,195,006 to Bowers and Clare describes an article inventory control system for articles, such as books and the like, for use in a library. This system uses RFID tags attached to each article and each tag has a unique identification number for identifying the individual article. An inventory database tracks all of the tagged articles and maintains circulation status information for each article. Articles are checked out of the library using a patron self-checkout system. Checked out articles are returned to the library via patron self-check in devices, however, these devices do not have the capability of automatically updating a patron's account to reflect a timely return of an article.
U.S. Pat. No. 6,204,764 to Maloney describes an object tracking system for tracking the removal of objects from a location and the replacement of the objects at the location. The system includes a number of RFID tags, each attached to one of the objects to be tracked. When activated, the RFID tag of an object transmits a unique code identifying the object. A storage unit is provided at the location and the storage unit has a plurality of receptacles configured to receive objects replaced at the location. A computer-based controller is configured to receive the transmitted codes and determine, based thereon, the absence or presence and location of objects within the storage unit. However, no facilities are provided for automatically updating or crediting a user's account to reflect return of a tagged item.